[Bug libstdc++/103340] New: constexpr std::string is incompatible with --enable-libstdcxx-allocator

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103340

            Bug ID: 103340
           Summary: constexpr std::string is incompatible with
                    --enable-libstdcxx-allocator
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

Only __gnu_cxx::new_allocator is usable in constant expressions. We need to
either disable constexpr std::string when other allocator base classes are
used, or make the changes needed to all/some of the allocator base classes to
e.g. add constexpr destructors.